It’s a nasty, two-man race. One candidate is a rich businessman accused of hiding his tax returns. The other is a longtime politician and lobbyist.

The controversies of the Republican presidential contest are trickling down into a Democratic primary fight playing out in Washington’s back yard — the previously conservative and rural Maryland district of Rep. Roscoe G. Bartlett (R), now redrawn to be a suburban battleground.

State Senate Majority Leader Robert J. Garagiola (Montgomery) and John Delaney, the founder of the Chevy Chase commercial lending firm CapitalSource, are gunning for the Democratic nomination for a seat their party views as one of its best November pickup opportunities.

Taking its cue from the opponents of former Massachusetts governor Mitt Romney, the Garagiola campaign has been needling Delaney for weeks to release his tax returns. Saying he wanted “to focus on the real issues,” Delaney on Wednesday released a summary of his returns from 2004 to 2010.

Over that seven-year period, Delaney made an average of $14.5 million per year and paid an average of $2 million in taxes, giving him an effective tax rate of just under 14 percent. That’s similar to the rate paid by Romney, who has been attacked by Democrats and some fellow Republicans for paying a lower rate than many other Americans.

As with Romney, Delaney made most of his money from investments, and capital gains are taxed at a lower rate than wages are. Delaney also said he gave an average of $2.75 million per year — or 19 percent of his income — to charity.

Unlike Romney, who released full tax returns numbering hundreds of pages, Delaney released only a broad summary that does not indicate exactly how Delaney made his money or where he keeps it. Romney’s returns sparked controversy in part because they showed he has had bank accounts in tax havens such as Luxembourg and the Cayman Islands. Delaney said he did not have any money in offshore accounts.

Garagiola — who works as a lawyer and serves in the Senate — released several years’ worth of tax returns last month. In 2010, he and his wife earned more than $200,000 and paid roughly $30,000 in taxes. His campaign called Delaney’s disclosure woefully lacking.

“What John Delaney disclosed is pathetic, not even enough information to get a credit card,” Garagiola campaign manager Sean Rankin said. “His partial disclosure is meant to hide a troublesome truth — tens of millions of dollars in taxes that he never paid because people like him and Mitt Romney game the system for their own personal gain.”

The focus on candidates’ wealth is an offshoot of the broader national debate about income equality, which was spotlighted by the Occupy Wall Street movement and has also been a frequent talking point for President Obama.

The Obama administration has pushed for the adoption of the Buffett rule to prevent wealthy people — such as investor Warren Buffett — from paying lower tax rates than their secretaries. Obama has called for those making $1 million or more to pay a tax rate of at least 30 percent.

Delaney said he would back that proposal and agreed with Buffett’s overall position on the subject. “In general, I’m for higher taxes on the wealthy,” Delaney said.

Like Romney, Delaney has tried to leverage his experience in the private sector to project the image of an outsider who can fix Washington. Just as Romney attacked former House speaker Newt Gingrich for his long tenure in the nation’s capital, Delaney has said he is “running against a career politician who has learned how to shake the special interest money tree.”

Adding to Garagiola’s supposed “insider” status is that the 6th District was drawn to be hospitable to him by his close ally, state Senate President Thomas V. Mike Miller Jr. (D-Calvert), and that Garagiola had previously worked as a lobbyist for the powerhouse firm Greenberg Traurig. (Garagiola’s lobbying experience is not mentioned on his official campaign biography.)

David Winston, a Republican pollster, said that in the current climate, candidates’ personal backgrounds would not be nearly as interesting to voters as their policy positions. “What people really want to know is, ‘What’s your plan to deal with jobs and the economy?’ ” Winston said.

Delaney’s wealth has a practical relevance in the 6th District race. Garagiola is familiar to some voters because of his service in the Senate, and he has the backing of much of the local party establishment and some key unions. Delaney has none of those advantages, but he does have millions of dollars to pour into campaign mailings and advertising.

While Delaney, Garagiola and three other candidates battle for the Democratic nomination, Bart­lett has a fight of his own. The veteran Republican faces a primary challenge from seven candidates, including state Sen. David R. Brinkley (Frederick) and Del. Kathy Afzali (Frederick).